Anne M. Grillet

Critical conditions for ferric chloride‐induced flocculation of freshwater algae

The effects of algae concentration, ferric chloride dose, and pH on the flocculation efficiency of the freshwater algae Chlorella zofingiensis can be understood by considering the nature of the electrostatic charges on the algae and precipitate surfaces. Two critical conditions are identified which, when met, result in flocculation efficiencies in excess of 90% for freshwater algae. First, a minimum concentration of ferric chloride is required to overcome the electrostatic stabilization of the algae and promote bridging of algae cells by hydroxide precipitates. At low algae concentrations, the minimum amount of ferric chloride required increases linearly with algae concentration, characteristic of flocculation primarily through electrostatic bridging by hydroxide precipitates. At higher algae concentrations, the minimum required concentration of ferric chloride for flocculation is independent of algae concentration, suggesting a change in the primary flocculation mechanism from bridging to sweep flocculation. Second, the algae must have a negative surface charge. Experiments and surface complexation modeling show that the surface charge of C. zofingiensis is negative above a pH of 4.0u2009±u20090.3 which agrees well with the minimum pH required for effective flocculation. These critical flocculation criteria can be extended to other freshwater algae to design effective flocculation systems. Biotechnol. Bioeng. 2012; 109:493–501.

Measuring the Thermal Conductivity of Porous, Transparent SiO2 Films With Time Domain Thermoreflectance

Nanocomposites offer unique capabilities of controlling thermal transport through the manipulation of various structural aspects of the material. However, measurements of the thermal properties of these composites are often difficult, especially porous nanomaterials. Optical measurements of these properties, although ideal due to the noncontact nature, are challenging due to the large surface variability of nanoporous structures. In this work, we use a vector-based thermal algorithm to solve for the temperature change and heat transfer in which a thin film subjected to a modulated heat source is sandwiched between two thermally conductive pathways. We validate our solution with time domain thermoreflectance measurements on glass slides and extend the thermal conductivity measurements to SiO 2 -based nanostructured films.

Ultra-low thermal conductivity of ellipsoidal TiO2 nanoparticle films

We report on the thermal conductivity of a series of convectively assembled, anisotropic titania (TiO2) nanoparticle films. The TiO2 films are fabricated by flow coating a suspension of ellipsoidal colloidal nanoparticles, resulting in structured films with tailored orientational order. The thermal conductivities depend on nanoparticle orientation and can be less than amorphous TiO2 films due to inter-nanoparticle boundary scattering. This nanoparticle ordering presents a unique method for manipulating the thermal conductivity of nanocomposites.

A level set approach to 3D mold filling of Newtonian fluids.

Filling operations, in which a viscous fluid displaces a gas in a complex geometry, occur with surprising frequency in many manufacturing processes. Difficulties in generating accurate models of these processes involve accurately capturing the interfacial boundary as it undergoes large motions and deformations, preventing dispersion and mass-loss during the computation, and robustly accounting for the effects of surface tension and wetting phenomena. This paper presents a numerical capturing algorithm using level set theory and finite element approximation. Important aspects of this work are addressing issues of mass-conservation and the presence of wetting effects. We have applied our methodology to a three-dimension model of a complicated filling problem. The simulated results are compared to experimental flow visualization data taken for filling of UCON oil in the identical geometry. Comparison of simulation and experiment indicates that the simulation conserved mass adequately and the simulated interface shape was in approximate agreement with experiment. Differences seen were largely attributed to inaccuracies in the wetting line model.Copyright

Three dimensional drop tracking flow chamber for coalescence studies

We have developed a novel flow chamber which imposes a controlled axisymmetric stagnation flow to enable the study of external flow effects on coalescence dynamics. This system allows for the first time the precise positioning of a drop in a three dimensional flow and additionally enforces a highly symmetric flow around the drop. We focus on the study of a single drop approaching a stationary flat plane as this is analogous to two drops approaching each other. A single drop is created and then guided along the unsteady center line of a stagnation flow. The real time computer control algorithm analyzes video images of the drop in two orthogonal planes and manipulates flow restricting valves along the four outlets of the flow. We demonstrate using particle image velocimetry that the computer control not only controls the drop position but also ensures a symmetric flow inside the flow chamber. This chamber will enable a detailed investigation of the drainage of the thin film between the drop and the lower surface in order to probe the effect of external flow on coalescence.

Tunable Thermal Conductivity of TiO2 Films of Close-Packed Nanoparticles

We report on the ultra-low thermal conductivity of a series of convectively assembled, anisotropic titania (TiO2 ) nanoparticle films. The TiO2 films are fabricated on aluminum coated glass substrates by flow coating a suspension of ellipsoidal colloidal nanoparticles, resulting in structured films with tailored order. Time domain thermoreflectance is used to measure the thermal conductivity of the TiO2 films. The thermal conductivities of these nanoparticle films are dependent on nanoparticle orientational order and films with more randomly oriented particles exhibit thermal conductivities less than the amorphous limit.Copyright

Optical Measurements of the Thermal Conductivity of Porous SiO2 Films

Nanocomposites offer unique capabilities of controlling thermal transport through the manipulation of various structural aspects of the material. However, measurements of the thermal properties of these composites are often difficult, especially porous nanomaterials. Optical measurements of these properties, although ideal due to the noncontact nature, are challenging due to the large surface variability of nanoporous structures. Recently, a novel pump-probe geometry was used in Time Domain Thermoreflectance (TDTR) to determine the thermal conductivity of liquids. In this work, we develop a thermal algorithm to solve for the temperature change and heat transfer in this TDTR geometry in which a thin film which is subjected to a modulated heat source is sandwiched between two thermally conductive pathways. We validate our thermal algorithm with TDTR measurements of the thermal conductivity and on a series of porous SiO2 -based nanostructured films.Copyright

Nano-Engineering by Optically Directed Self-Assembly

Lack of robust manufacturing capabilities have limited our ability to make tailored materials with useful optical and thermal properties. For example, traditional methods such as spontaneous self-assembly of spheres cannot generate the complex structures required to produce a full bandgap photonic crystals. The goal of this work was to develop and demonstrate novel methods of directed self-assembly of nanomaterials using optical and electric fields. To achieve this aim, our work employed laser tweezers, a technology that enables non-invasive optical manipulation of particles, from glass microspheres to gold nanoparticles. Laser tweezers were used to create ordered materials with either complex crystal structures or using aspherical building blocks.

Measurements of Wall Slip during Rise of a Physically Blown Foam

Polymeric foam systems are widely used in industrial applications due to their low weight and abilities to thermally insulate and isolate vibration. However, processing of these foams is still not well understood at a fundamental level. The precursor foam of interest starts off as a liquid phase emulsion of blowing agent in a thermosetting polymer. As the material is heated either by an external oven or by the exothermic reaction from internal polymerization of the suspending fluid, the blowing agent boils to produce gas bubbles and a foamy material. A series of experiments have been performed to allow observation of the foaming process and the collection of temperature, rise rate, and microstructural data. Microfocus video is used in conjunction with particle image velocimetry (PIV) to elucidate the boundary condition at the wall. These data provide input to a continuum level finite element model of the blowing process. PIV is used to measure the slip velocity of foams with a volume fraction range of 0.5...

A multiscale approach to multi-component wetting.

Laser scanning confocal microscopy has been applied to study segregation in multi-component wetting. By labeling the two components of a blend with contrasting fluorescent dyes, the approximate local concentration can be determined from the relative fluorescence intensities. As a proof of concept, a coarsely blended mixture was imaged and parameters were adjusted to achieve good spectral separation of the two components. The technique was then applied to a well-blended drop of the two components and one component was observed to segregate to the air interface.Copyright